25 April 2017

Fossil groundwater vulnerable to modern contamination

A new study shows that over half of global groundwater is over 12,000 years old

© Subway Slot Canyon in Zion National Park | Shutterstock

© Subway Slot Canyon in Zion National Park | Shutterstock

Fossil groundwater is water which has been stored beneath the earth's surface for more than 12,000 years. The new study found that fossil groundwater makes up a significantly higher proportion of the earth’s groundwater, than previously thought. It also found that this ancient water is not immune to modern contamination, as has been widely assumed.

This study, led by University of Calgary hydro-geologist Scott Jasechko and co-authored by an international team of researchers, is published online today (April 25) in Nature Geoscience. IIASA Water Program Deputy Director Yoshihide Wada contributed to the study. He says “The findings of this study have important ramifications on how we should use groundwater in the future and highlight the urgent need for groundwater management”. Wada highlighted that groundwater used for irrigation is a particular concern, due to the fact that it has previously been assumed to be a high quality water source and is often un-tested before being used to produce food.

Groundwater is the water stored beneath the earth's surface in soil pore spaces and within the fractures of rock formations. It provides drinking and irrigation water for billions of people around the world.

Jasechko and his co-researchers dated groundwater from over 6,000 wells around the globe. By measuring the amount of radioactive carbon in the water, the team was able to determine the age of the groundwater. They discovered that the majority of the earth's groundwater is likely fossil groundwater, derived from rain and snow that fell more than 12,000 years ago. Jasechko and his team have determined that this fossil groundwater accounts for between 42 to 85 per cent of total fresh, unfrozen water in the upper kilometre of the earth's crust.

Until now, the scientific community has believed that this fossil groundwater was safe from modern contamination, but Jasechko's study has proved otherwise.

"The unfortunate finding is that even though deep wells pump mostly fossil groundwater, many still contain some recent rain and snow melt, which is vulnerable to modern contamination," says Jasechko. "Our results imply that water quality in deep wells can be impacted by the land management decisions we make today."

Jasechko explains rain and snow that fell after the 1950s contains tritium, a radioactive isotope that was spread around the globe as a result of thermonuclear bomb testing. Disturbingly, traces of tritium were found in deep well waters, which indicates that contaminated rain and snow melt of today may be able to mix in with deep fossil groundwater and, in turn, potentially contaminate that ancient water, thought to be pure. 

"The upshot is that when we use fossil groundwater we should consider water quality risk in addition to sustainable use,” he says. "We may do well to develop land management plans that protect fossil groundwaters from pollutants so that these resources are available for future generations.


Text adapted from the University of Calgary Press Release by Heath McCoy 


Reference

Jasechko S, Perrone D, Befus KM, Bayani Cardenas M, Ferguson G, Gleeson T, Luijendijk E, McDonnell JJ, et al. (2017). Global aquifers dominated by fossil groundwaters but wells vulnerable to modern contamination. Nature Geoscience 10 (6): 425-429. DOI:10.1038/ngeo2943.


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Last edited: 25 April 2017

CONTACT DETAILS

Yoshihide Wada

Deputy Program Director

Water

T +43(0) 2236 807 241

Water Program

PUBLICATIONS

Vanham D, Hoekstra AY, Wada Y, Bouraoui F, de Roo A, Mekonnen MM, van de Bund WJ, Batelaan O, et al. (2018). Physical water scarcity metrics for monitoring progress towards SDG target 6.4: An evaluation of indicator 6.4.2 “Level of water stress”. Science of the Total Environment 613: 218-232. DOI:10.1016/j.scitotenv.2017.09.056.

Dos Santos S, Adams EA, Neville G, Wada Y, de Sherbinin A, Mullin Bernhardt E, & Adamo SV (2017). Urban growth and water access in sub-Saharan Africa: Progress, challenges, and emerging research directions. Science of the Total Environment 607: 497-508. DOI:10.1016/j.scitotenv.2017.06.157.

Mehran A, AghaKouchak A, Nakhjiri N, Stewardson MJ, Peel MC, Phillips TJ, Wada Y, & Ravalico JK (2017). Compounding Impacts of Human-Induced Water Stress and Climate Change on Water Availability. Scientific Reports 7 (1): e6282. DOI:10.1038/s41598-017-06765-0.

Felfelani F, Wada Y, Longuevergne L, & Pokhrel YN (2017). Natural and human-induced terrestrial water storage change: A global analysis using hydrological models and GRACE. Journal of Hydrology 553: 105-118. DOI:10.1016/j.jhydrol.2017.07.048.

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